Flow control valves are well known in irrigation systems. They are used to control the flow of pressurized water through a pipe and thereby allow sprinklers fed by the pipe to be turned on and off. Such valves are often remotely controlled by control signals sent from an automated irrigation controller. For example, the controller might send an electric actuating signal to a solenoid that is part of the valve to allow the valve to open.
One type of solenoid operated valve is shown in U.S. Pat. No. 4,505,450 to Saarem et al. This valve is made from two parts, namely a body portion in which the inlet, outlet and valve seat are formed and a separable cap on which an actuating solenoid is carried. A flexible diaphragm engages the valve seat to close the valve. A bleed tube assembly is supported in a support bracket in the valve body. The bleed tube assembly has an upper end located in a pressure chamber above the diaphragm and a lower end located below the diaphragm. The solenoid plunger normally seals against the upper end of the bleed tube to keep the valve closed. When the solenoid is actuated by a control signal, the plunger lifts up off the bleed tube to allow fluid pressure to bleed out of the pressure chamber, thereby opening the valve.
One difficulty of this prior art valve is that the length of the bleed tube must be precisely controlled during manufacture, and the bleed tube must be precisely installed in the support bracket during assembly or replacement thereof, to allow proper operation of the valve. This is difficult to do, particularly when working without special tools when replacing the bleed tube i the field. For example, if the bleed tube is not pushed into the support bracket to exactly the proper depth, then it may be too long and jam the solenoid plunger. Alternatively, if the bleed tube is made too short, or if it is inadvertently pushed down into the support bracket too far, then the plunger will never be able to close the bleed tube, leading to improper operation. Moreover, flexure of the cap of the valve, due for example to heat absorption, may cause the plunger to become misaligned with the bleed tube of the prior art valve, even when the valve was initially properly manufactured or serviced.